1. Field of the Invention
The present invention relates to an organic light emitting display device and a driving method thereof.
2. Description of Related Art
In recent years, flat panel display devices having reduced weight and volume in comparison to a cathode ray tube (CRT) have been developed. The flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display, etc.
Among the flat panel displays, the organic light emitting display displays an image using organic light emitting diodes (OLEDs) that emit light through the recombination of electrons and holes. The organic light emitting display has advantages such as rapid response time and low power consumption.
Pixels in conventional organic light emitting display devices utilizing an analog drive system display an image by charging a storage capacitor (Cst) in each of the pixels with a predetermined voltage and supplying an electrical current, which corresponds to the charged voltage, to the OLEDs. The analog drive system may have difficulty uniformly displaying an image due to variations in the threshold voltage and mobility of the drive transistors between the pixels.
Organic light emitting displays utilizing a digital drive system rather than an analog drive system may more uniformly display an image. The digital drive system supplies data signals to each of the pixels, wherein the data signals correspond to turn-on and turn-off states, and displays gray levels by controlling the time that the pixels are turned on during a frame that is time-divided into a plurality of subframes. The digital drive system may display an image uniformly regardless of the variations of the drive transistors between the pixels.
Digital drive systems may have difficulty supplying a correct data signal to each of the pixels utilizing a demultiplexer since the digital drive system is driven with one frame being time-divided into a plurality of subframes. In conventional digital drive systems, the demultiplexer has been used to reduce the number of channels in the data drivers. The demultiplexer transfers a data signal to a plurality of data lines, wherein the data signal is supplied to an output end of each of the data drivers.
In a conventional digital drive system, wherein the number of the subframes in one frame is 15 and a first horizontal period is set to approximately 1.39 μs in driving a 3-inch WVGA panel (800×480 RGB), the demultiplexer (for example, a 1:2 demultiplexer) transfers a data signal, which is supplied to one output line, to two data lines during one 1.39 μs horizontal period.
Each of the pixels is supplied with a data signal during ½ of the horizontal period when the data signal is transmitted to two data lines using a demultiplexer. Accordingly, the data signal may not be supplied to the pixels for a sufficient amount of time. In particular, the use of the demultiplexer requires some additional time in the horizontal period to ensure a drive margin of a switch that is included in each of the channels.